Like Lightning

Despite the capabilities of state-of-the-art animation software and talented computer artists, starring roles in weekly live-action television shows have been virtually non-existent for digital characters. This is because of the daunting production logistics and formidable creative and technical challenges imposed by the medium's limited budgets and tightly compressed shooting schedules. However, a digital cast of computer game characters in the new children's television series Ace Lightning is redressing that situation, and in doing so, is paving the way for more virtual actor roles (see "A New Hybrid," pg. 44).

Now airing in the UK and Canada, and set to debut later this year in the US, Ace Lightning presents a rare and seamless co-existence of live action and CGI on weekly television. Created by Calibre Digital Pictures in Toronto, each half-hour episode features more than 10 minutes of digital content, including nearly 160 shots of engaging character animation, realistic effects, digital matte paintings, and greenscreen composites. To accomplish this feat, Calibre designed a production pipeline that is streamlined to accommodate the strict time frame of a series and flexible enough to let the artists collaborate with the film crew, so they can more easily composite the CGI into the shots.

With a streamlined production pipeline, Calibre Digital Pictures is meeting the challenges of using digital characters in a weekly television series. In Ace Lightning, the leading roles are played by a live actor and two CG characters¿the hero, Ace

The live star of the series is 13-year-old Mark Hollander, whose life is turned upside down when characters from his favorite computer game exit their cyber world and land in his backyard. First to arrive is the evil Lord Fear and his motley gang of henchmen, who are hotly pursued by Mark's favorite superhero, Ace Lightning. Believing he's just landed in another level of the game, and that Mark is a fellow Lightning Knight, Ace enlists the youngster to help him battle the villains.

The show's digital troupe currently features a bizarre assortment of computer-generated characters, including Lord Fear, a skeleton with telescoping arms that coil around his victims. Plotting his evil deeds with histrionics, he commands a group of creatures that can morph into various attractions at the local carnival to avoid detection. They include Staff Head, a bat-like creature perched atop Lord Fear's wooden staff; Lady Illusion, a voluptuous woman who can assume animal forms; Anvil, a rhino-headed oaf that morphs into the test-your-strength booth; Pigface, a pig-headed monster that transforms into a trash bin; and Dirty Rat, a flying spy that turns into a gargoyle overlooking the carnival's haunted house.

Working in Alias Systems' Maya, the artists at Calibre specifically develop the show's character models for broad, physical expression. The team initially sculpts the meshes with NURBS and subdivision surfaces, both of which are ideal for modeling organic surfaces, then converts them into closed-surface polygonal models that are more efficient and easier to work with.

Because the CG characters are intended to appear native to the digital realm, their texturing is accomplished with standard Maya shading networks consisting of color, bump, and specular maps. However, more complex shading networks are required for the scale models of the live-action sets and props, which also are built for previsualizing the scenes and assisting the lighting and compositing departments with shadow casting and reflection mapping. Special care is taken in texturing these models, especially those with glass, metallic, and plastic surfaces, which have to be intercut with a live-action counterpart. Other props demand animated textures and skeletal rigs with keyframeable controls, such as the glass orb crowning Staff Head, which is mapped with a cloud texture that brightens before expelling an energy bolt.

In addition to creating the CG characters, including Lord Fear (above), the artists built a number of complex 3D objects and set pieces, some of which required animated textures and skeletal rigs controlled through keyframes.

After the artists complete the models, they generate a master file of customized character setups. Then, following every Ace Lightning episode, the team adds a new version of each character—specially modeled or rigged to accommodate the unique demands of that particular show—to the master file, enabling the animators to later choose a model that meets the needs of a certain scene. Maintaining this expanding database of custom setups also allows the artists to continually improve the character rigs over the course of the series.

Each of these character models contains approximately 80 joints, used for animation. The base skeletal setup comprises two sets of joints for the limbs: one for binding the geometry and inverse kinematics (IK), and the other for the forward kinematics (FK). Using a combination of constraints and Maya Set Driven Keys to keep the twin joints in perfect alignment, the animators operate an IK/FK toggle switch to shift between them and keyframe either set.

According to technical directors Yi Zhao and Daniel Lu, much of Calibre's character rigging hinges on well-placed Maya Set Driven Keys. By manipulating a series of elemental blend shapes for the face, the team creates Set Driven Key controls to achieve a wide range of movements for many of the facial features, including the lip sync. In total, 30 controls are used for Ace Lightning's facial expressions, 20 for Lady Illusion's, and 10 for Staff Head's.

Once the CGI superheroes and villains are modeled, rigged, and ready to take on the real world, Calibre's artists tackle the real technical feat of the show: the planning and execution of each episode's 10 minutes of composited effects and character animation. "It's important to the overall production that Calibre get involved early in the script-writing process," notes animation director Robert D.M. Smith. "It is crucial to flag pitfalls that could put us behind in production, such as shots featuring interactions between live actors and CGI characters, and scenes involving interactions with natural elements like water."

At the outset of pre-production, a CG artist creates storyboards to indicate the movements of the camera and the actors, establishing camera placements that will ideally situate the real actor behind the CG character or at a distance where the actor's gestures will not "screen" the CG character and result in a difficult matte.

To ensure that the CGI integrates perfectly with the live action, Calibre's onset visual effects supervisor records the camera's focal length, rotation, and height up to the nodal point, and transfers the information to the Maya camera. Occasionally, the focal length of the virtual camera is increased to cope with the extreme foreshortening in scenes that are deliberately shot with a wide-angle lens to accommodate digital camera moves created in Discreet's combustion. The onset visual effects supervisor also records the lighting design for every scene and, in some cases, for individual shots, since many of the same scenes are filmed at different times of day and in different weather conditions.

Each character model is designed and rigged to accommodate the specific demands of each episode. The new versions are later added to a master library of customized character setups for use in future shows.

Like the characters, the effects used in the show also are a mix of real (practical) and digital. For nearly every episode, the artists add animated effects, including sparks, fireworks, smoke, lightning, exploding crystal balls, and myriad other electrical, pyrotechnical, and dust effects, all generated in Discreet's flame. Currently, the digital elements are rendered on both Linux- and Windows 2000-based workstations running Maya 3.0. Although the renderfarm is quick and efficient for generating full-resolution dailies, the studio is currently integrating the Maya, mental ray (Mental Images), and 3ds max (Discreet) renderers through a number of scripted GUIs to form a more robust and powerful pipeline.

One of the most ambitious integrations of practical and CG effects thus far required Ace to fall onto the roof of a car, causing it to collapse. To accomplish the stunt, the team initially contemplated cross-dissolving between two images of a normal and crushed roof, but decided that a more convincing shot could be achieved by dropping a 150-pound weight from a height of 30 feet onto the car roof and compositing Ace into the film plate. Fortunately, it not only collapsed the roof at an angle that afforded a full view of Ace sprawled unceremoniously on his back, but fell deep enough into the car so that it was barely visible. Then, back at Calibre's studio, an artist animated Ace so that his falling body hid the descent of the weight and tracked with the bounce of the car. The artist also painted out and replaced the shadows and reflections of the weight with those of Ace by modeling geometry that approximated the roof, windshield, and trunk, and adjusting the position and intensity of the lights to maximize the surfaces' reflectivity before rendering Ace's reflective pass. Finally, the team enhanced the concussive force of the impact with flying debris created in combustion.

For one of the show's most demanding sequences, artists had to integrate digital and practical effects to achieve the illusion of having the CG hero crashing through the roof of an actual vehicle.

Ace Lightning is pushing the broadcast envelope with a large cast of major digital players with multifaceted personalities. It also breaks the mold through its use of sophisticated compositing—involving live action unfolding in a wide range of sets, locations, and weather conditions—and digital stunt work typically reserved for feature-film production. "Viewers are well versed in CGI," says executive producer Pete Denomme, "so we knew that the show's success—in particular, its ability to hold the audience—rested on the credibility of our hybrid scenes."

Part of the show's believability stems from the writing, acting, and a premise that calls for computer graphics in every story line. Yet the ability to suspend the audience's disbelief is ultimately the result of the effects artists' efforts to seamlessly wed the live action and CG, and craft unique performances for every scene that are not only highly expressive, but also acutely sensitive to the real actors' performances—all under the most pressured production conditions.

For this live-action environment scene, the artists used proxy models of Ace Lightning (left) and Pigface (right) before finalizing the scene.

Martin McEachern, a contributing editor forComputer Graphics World, can be reached at martin@globility.com.